ASTRONOMICAL DISCOVERIES. 77 



I was never able to detect any trace of lateral refraction on 

 the declivities of the Andes, or during the frequent mirages 

 in the torrid plains or Llanos of South America, notwith- 

 standing the heterogeneous mixture of unequally heated 

 atmospheric strata. As the Peak of Teneriffe is so near us, 

 and is so frequently as* ended before sun-rise by scientific 

 travellers provided with instruments, I would hope that this 

 reiterated invitation on my part to the observation of the 

 undulation of the stars may not be wholly disregarded. 



I have already called attention to the fact that the basis 

 of a very important part of the astronomy of our planetary 

 system was already laid before the memorable years 1608 and 

 1610, and therefore before the great epoch of the invention of 

 telescopic vision, and its application to astronomical purposes. 

 The treasure transmitted by the learning of the Greeks and 

 Arabs, was augmented by the careful and persevering labours 

 of George Purbach, Regiomontanus (. e. Johann Miiller) and 

 Bernhard Walther of Niirnberg. To their efforts succeeded a 

 bold and glorious development of thought the Copernican 

 system ; this again was followed by the rich treasures derived 

 from the exact observations of Tycho Brahe, and the combined 

 acumen and persevering spirit of calculation of Kepler. Two 

 great men, Kepler and Galileo, occupy the most important 

 turning-point in the history of measuring astronomy ; both 

 indicating the epoch that separates observation by the 

 naked eye, though aided by greatly improved instruments of 

 measurement, from telescopic vision. Galileo was at that 

 period forty-four, and Kepler thirty-seven years of age ; Tycho 



mique et geog^ vol. ii. 1819, p. 84.) Brandes (Gehler's 

 Umgearb. phys. Wortersb, bd. iv s. 549) refers the pheno- 

 menon to mirage. The star-like heliotrope light has also 

 frequently been seen, by the admirable and skilful observer, 

 Colonel Baeyer, to oscillate to and fro, in a horizontal 

 direction. 



